Process for treatment of vanadium containing fly ash

ABSTRACT

The invention is addressed to the recovery of vanadium by the treatment of fly ash derived from bituminous or petroleum products, such as bituminous schists. In accordance with the practice of this invention, the fly ash is treated with a concentrated caustic soda solution selectively to solubilize vanadium, and in adding calcium oxide to the reacting solution in an amount within the range of 6-40 percent of the silica contained in the ash, with the addition being made preferably during the latter portion of the treatment.

United States Patent 1191 Guillaud 1 1 Mar. 25, 1975 PROCESS FORTREATMENT OF 3,416,882 12/1968 Whigham 423/64 x V D CONTAINING FLY ASH3,712,942 l/l973 Suejda 423/68 X [76] Inventor: Philippe Guillaud, 1e

Giff .M i i B ill Primary ExaminerHerbert T. Carter France [22] Filed:June 8, 1973 [57] ABSTRACT [21 A 1. No.: 368 053 1 pp The 1nvent1on 1saddressed to the recovery of vanadium by the treatment of fly ashderived from bitumil Foreign Appllcatlon y Data nous or petroleumproducts, such as bituminous June 9, 1972 France 72.20907 schists. Inaccordance with the practice of this invention, the fly ash is treatedwith a concentrated caustic [52] U.S. Cl. 423/65, 423/68, 423/331 sodasolution selectively to solubilize vanadium, and in [51] Int. Cl. C0lg31/00 adding calcium oxide to the reacting solution in an [58] Field ofSearch 423/62, 66, 68, 65 amount within the range of 6-40 percent of thesilica contained in the ash, with the addition being made [56]References Cited preferably during the latter portion of the treatment.

UNITED sTATEs PATENTS 8 Cl 3 D 1.563.061 11/1925 Baldeschwieler 423/64SI 03 108.0 1 0 103p lTON 0F Nat-IE5 FerOg 57.0

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R CIPIT y V105 6.01% FILTERINCI 2 NMHINGSIFILTER .LEAN warm 0.101175.61% eat 32 n 0 HETREATHENT vurru tam/macaw!) :1 mum MR 2 51925 SHEET1 BF 3 FIG. I

5TOICHIOMETRIC QUANTITY OF LIME TWICE STOlCHIOMETRIC QUANTITY OF LINErune. (HQURS) PROCESS FOR TREATMENT OF VANADIUM CONTAINING FLY ASH Thepresent invention relates to a process for treatment of fly ash derivedfrom bituminous or petroleum products for the purpose of solubilizingthe vanadium present as a vanadate.

The ash contains 20-70 percent free carbon with the remainder comprisingmineral matter composed mainly of silica and alumina and up to 15percent by The raw material, for which the process of this invention hasbeen devised, is formed of fly ash produced by the combustion of cokeprepared from bituminous schists, a typical analysis of which is asfollows by weight): 2% V 20% SiO- A1 0 4% Fe O 3% C210, 1% TiO 1 to 2%MgO Na O K 0, the remainder being essentially free carbon. However, theprocess can also be used with all kinds of fly ash produced by thecombustion of petroleum products or coke derived from vanadiumcontaining petroleum products, for which known processes have not beenfound to be suitable.

The process most commonly used, for recuperating vanadium from minerals,consists in treating the later with sulphuric acid. This type oftreatment is described in Canadian Patent No. 770,058; however, it isnot suitable for the treatment of ash containing small amounts ofvanadium because, on the one hand, of the high consumption of reactantswhich react with the oxides and, on the other hand, the difficulty oflater separating vanadium from the dissolved salts of iron and aluminum.

Roasting in the presence of a salt of sodium can be used in certaincases; however, it is a costly operation which is applicable only to ashhaving high vanadium content. The operating conditions, in this case,are very complicated since the roasting temperature must be kept withina very narrow range. 1

Attack by a solution of sodium hydroxide, either after calcination inthe presence ofa sodium salt (Russian Patent No. 172,044), or on thecrude ore (U.S. Pat. No. 1,563,061), could be considered. Such processis applicable only to usual ores rich in vanadium and poor in silica andalumina, since both of these substances go into solution together withvanadium and subsequent separation is difficult.

It has been proposed (in German patent application No. 1,767,408) toeffect reaction with milk of lime which first precipitates calciumaluminate and calcium silicate, then cooling after filtering tocrystalize an alkaline vanadate. Such a process is long and expensive inview of the various successive filtrations. Furthermore, it is somewhatselective: a portion of the vanadium is carried off with the calciumaluminates and calcium silicates and the alkaline vanadate obtained isimpure and difficult to purify.

1f the V O /SiO weight ratio in the raw material is about 0.1, it ispossible to obtain a concentrated solution which contains more vanadiumthan silica, in the fraction which is dissolved, only if the rate ofsolubilization of vanadium is more than ten times greater than that ofsilica. The alkaline treatment of raw materials of this type isdifficult because one must, at the same time, obtain an extremely highrate of solubilization of vanadium and a very low rate of solubilizationofsilica.

The present invention is based upon the observation that if the free ashis treated with a caustic soda solution containing 1 to 5 moles NaO/liter, vanadium is much more easily solubilized than silica, alumina,and the other impurities. It has futhermore been observed that thesolubilization is selective in practice. This was wholly unexpected bythe skilled in the art.

For example, when free ash containg 2% V 0 18% SiO 10% A1 0 4% Fe- 0 and60% carbon are treated at C with a 2.5 M solution of NaOH, after 6hours. 85 percent vanadium and only 7 percent silicon have beensolubilized, while treatment of classical types of minerals, vanadiumand silicon were solubilized in substantially equal percentages.

In order to try to provide an explanation for this unexpected behavior,tests were made under the electronic microscope. These tests have shownthat the particles of ash, which are usually in the form of hollow orsolid balls of about 10 microns diameter, possess a vitreous aspect and,after reaction with caustic soda, have an engraved aspect withoutnoticeable variation in form and dimension. It is therefore believed,and this is submitted as a non-limiting hypothesis, that vanadium is notdispersed throughout the whole vitreous mass within the particles, butrather it is located in se lective sites which are more accessible.

The process of this invention consists in combining an attack of the ashwith aqueous solution of sodium hydroxide, under certain conditions ofconcentration, temperature and time, with an addition of lime in aweight proportion of 6-40 percent of the weight of silica contained inthe ash, i.e. a quantity wholly insuffi cient to effect totalneutralization.

The ideal industrial conditions are not necessarily those which lead toa higher V O /SiO ratio in the dissolved phase, since one must also takeinto consideration the caustic soda consumption and, above all, theabsolute rate and amount of solubilization of vanadium, all of which arevery important factors in determining the cost ofthe vanadiumconcentrate. However, it has been observed that with concentrations over5 moles Na O per liter, the suspension remains undesirably viscous anddifficult to use. With concentrations less than 1 mole per liter,solubilization of vanadium is unsatisfactory, even after considerableperiods of time. It is desirable to operate with concentrations withinthe range of 3 to 5 moles Na O/liter, by the paste technique, i.e. witha high solid/ liquid ratio to give a suspension of pasty consistency. Inthis manner, it is possible to realize important savings of causticsoda, especially if this material is expensive. It is, however,preferable to operate in a liquid phase and with a concentration of l to2 moles Na 0 per liter. In this manner, the process is more easily putinto operation. Concentrations above 2 moles per liter provide for amore substantial solubilization of silica without a comparable increasewith respect to vanadium. The solid/liquid ratio should be as high aspossible with the required quantities of caustic soda while, at the sametime, enabling a fluid mixture to be obtained in spite of the eventualpresence of a large quantity of carbonaceous material which absorbs alot of water. A preliminary treatment, such as light roasting, and/orflotation, can also be carried out in order to eliminate residualcarbon, without being prejudicial to the operation of the process ofthis invention.

The total quanity of Na- O which should be used is usually about 25 to40 kg per kg of mineral material present in the ash and 20 to 30 kg forthe paste technique. The temperature at which the attack is carried outshould be above 50C., perferably between 80C and the boiling point. Atlower temperatures, the attack does not progress rapidly and it ispractically ofa quantity of calcium oxide within the range of 6-40percent of the weight of silica contained in the ash.

This is not the quantity which corresponds to the maximum V O /SiO ratioin the solution. The latter would be in the vincinity of 8.3 for about380 kg lime economy of caustic soda as well as the possible rate ofsolubilization of vanadium. It is preferred to make use non-existent atroom temperature. 5

Th attack, i d out under h conditions indi per ton of silica. In suchinstance, the loss of vanadium cated above, is continued for 4 to 8hours. It can be would be highachieved more rapidly with highlyconcentrated soluy y g the kinetics of the Precipitation P tions, Aft 8hours, little, if any, more is enon of vanadium and silicon, resultingfrom the treatd 10 ment with lime, in a solution obtained by treating aThe addition of line to the reaction solution materi- Caustic SedaSolution Without time, it has been unexally reduces stabilization ofsilica and alumina, duet to P y found that the Precipitation of theSilicate ill the formation of silicate and insoluble calciumsilicoequilibrium, was reached much more p y than thllt aluminate. Itwould appear logical to assume that there of the Vahadatewould be asimultaneous formation of insoluble calt the dtawmgs, Whleh e subhlittedy y i cium vanadate which would considerably decrease the e h t not byway of hmttatloh of the Praetlee 0t solubilization rate of vanadium.This does occur when thts thvehtlohi i the addition of lime is employedwithout resorting to 1 h w Curves telatlhg ppreelhltatloh P e theSpecial measures Outlined hereinbeiow drum and silica compounds as afunction of t1me 1n a A study was made of the influence of the additionof cohtalhmg 1,090 mg/l Y' 650 51 (3) increasing quantities of lime tothe caustic soda solum h Presence ofa stolchlometttc amount Ofhme, andtion at the start of the reaction. In a test corresponding (h) m ePresence of twtce that amount; to the ash used in Example 1 (hereinafterdescribed), 2 15 how gr m o treatment of fly ash in actable I shows thevariation in rate of solubility of vanacotdahce Wlth the processdescribed m P 1 of Exam dium and silicon and the consumption of causticsoda Ple l; I as a function ofthe concentration oflime, expressed as 3 ahow d'agram of the treatment desctthhd CaO. The last column, in thefollowing tabe, illustrates m part 2 h the weight ratio of V O /SiO inthe solution after reach Prectpltatloh 0f calclultt s llcates Occursvery tion, starting with a weight ratio of 0.1 in the raw mateh l f evenat the Start of the hme addthoh, whtle Pt riaL c1p1tat1on ofthe vanadatestarts only after a substantial TABLE I Quantity of lime (a0 V- .O SiO-Con- V 0 sumpexpressed in Kg/t of solubilized solubiltion silicacontained in in 71 of ized in 7! K SiO the ashes. added as V205 in ofSiO Na- /t solua whole at the start ashes in ashes bilized of thereaction It will be seen that the results are markedly improved periodof time, such as 30 to 60 minutes in the first case by adding more than60 kg of lime per ton of silica. with a stoichiometric amount of lime,and about 15 1 The quantity of solubilized vanadium decreases minutes inthe second case with twice that amount.

much less rapidly than the quantity of solubilized silica 55Modifications can be made to the process for addiwhen the quantity oflime is progressively increased up tional lime in order to obtain a highratio of V O /SiO to about 400 kg per ton of silica. Beyond this amount,in the solution without increasing the vanadium losses. vanadium becomesincreasingly insoluble. This modification consists in adding lime, notall at It is to be noticed that such amounts are considerably once inthe solution of caustic soda at the start of the less than thatnecessary to form calcium silicate with all reaction, but eitherprogressively during the reaction or of the silica present. Forinstance, 930 kg of lime per preferably all at once toward the end ofthe reaction, ton of silica would be necessary to obtain CaSiO such as15 to 30 minutes before filtering the mixture. The optimum economicefficiency from the lime ad- The latter procedure is easier in atreating apparatus in dition to the reacting solution is in the vicinityof about continuous operation. The following Table II shows the 300 kgof CaO per ton of silica, in view of the resulting results which areobtained by adding various charges of lime in the suspension after 5hours and 30 minutes of reaction which is terminated 30 minutes later.

TABLE II lime added 30 mn V solu- SiO solu- Con- V 0 sump beforefiltration, bilizcd in bilizcd in tion of SiO in kg for l t of /1 of V 07r in of caustic solubilsilica contained in ashes SiO. in soda kg izedin the ashes ashes Na O/t It will be seen that, under these conditions,the addition of 230 kg of lime per ton of silica has not only decreasedthe rate of solubilization of vanadium by 2 percent, but has decreasedthat of silica by 88 percent. The weight ratio V O /SiO in the solutionis in the vicinity of 10. The caustic soda consumption corresponds to 42kg per ton of treated ash.

Higher quantities of lime produce a slight increase of the ratio V- O/SiO in the solution, but lead to such large decrease in the rate ofextraction of the vanadium oxide as to be economical under actualconditions. Preferably, the quantity of calcium oxide should comprisebetween and percent ofthe weight of silica contained in the ash.

It is therefore possible to start the reaction with a solution ofcaustic soda alone, then, after filtration, treat the liquid phase withlime in order to precipitate the major portion ofsilica, withoutinsolubilizing a substantial portion ofvanadium. Thereafter, calciumsilicate is separated by filtration. Calcium vanadate is thenprecipitated by using excess lime for an extended period of time. Theprecipitate can be treated for example in known manner with carbondioxide and ammonia in order to precipitate ammonium vanadate.

However, this mode of operation produces an excessive consumptionofcaustic soda as a result of the formation of insoluble sodiumsilico-aluminates. Furthermore, the presence of two filtration stepsused in succession is complicated and undesirable. According to apreferred mode of operation of the process according to the invention,lime is caused to act directly on the product which is reacted withcaustic soda, before filtration. For this purpose, the entiresuspension, obtained by reaction with caustic soda, is treated while hotwith a milk lime containing 0.2 to 0.3 mole of CaO per mole of silicapresent in the treated ash. In this manner, the sodium silico-aluminatesare partially replaced by calcium silico-aluminates and nearly all thesodium silicate is precipitated in the form of calcium silicate. 20 tominutes after the addition of lime, the suspension is filtered while thesodium vanadate has not started to react with lime.

The filtered solution contains as much vanadium, but much more sodiumand much less silica than the filtered solution after reaction with thecaustic soda alone, without treatment with lime.

In a continuous industrial process, the reaction is carried out in aseries of reactors: the first reactors receive the ash and the solutionof caustic soda alone, which is present therein, while stirring duringan average of 5 to 6 hours at 80 to 90C. before transfer to the lastreactor. It is in the last reactor that lime is added as milk LII lime.The suspension resides therein for an average of 30 minutes, after whichit is filtered. Before removing the residue, the latter is washedthoroughly in order to displace the solution which is strongly held bythe carbon.

The filtrate, combined with the wash water, consists of an aqueoussolution which contains some vanadate, some sodium silicate and freecaustic soda. Since the solution is too diluted to be recycled, it isconcentrated to a third of its volume, as by evaporation.

The solution is then treated by processes known pe se in order toprecipitate the vanadium and to recover the caustic soda. The calciumsalts (V 0 4Ca0) and (CaSiO are precipitated by adding excess lime inorder to increase the speed and the rate of precipitation of the basiccalcium vanadate. It is believed to be undesirable to allow too muchincrease in the vanadium concentration of the solutions which arerecycled. The precipitation lasts about 2 hours at C in the presence ofa quantity of lime which is double the stoichiometric quantity andproduces an impure product which cannot generally be used in this form.

In order to separate the pure oxide, the precipitate is suspended in aknown manner in an aqueous solution of sodium bicarbonate and treated bybubbling carbon dioxide to cause a precipitation of calcium carbonateCaCO and of the residual silica. After filtration, washing andconcentration of he filtrate, as by evaporation, vanadium is allowed toprecipitate without heating in the form of ammonium metavanadate, byintroducing ammonia and carbon dioxide. The precipitate is separatedfrom the filtrate, which is recycled for carbonate formation, and isthereafter decomposed under heat to recover ammonia, which is recycled,and vanadium oxide.

As an example, the treatment was carried out with fly ash resulting fromthe combustion of coke derived from the treatment of bituminous schistsand containing, by weight, per kg of ash:

SK): M 0 l03 Fe o 37 C 210 26.3 V 0 19.5 TiO 10.7 MgO Na O K 0 15Various other oxides 3.5

Carbon 605 A portion of ash was treated according to the prior art byattack with sodium hydroxide alone. Another identical portion wastreated according to the present invention, by attack with sodiumhydroxide with an addition of lime.

The amounts mentioned hereinafter refer to 1,000 kg of ash but it willbe understood that the treatments are continuous.

EXAM PLE 1 Portion No. 1 (FIG. 2)

The reaction, with a liquor containing 116 kg Na O in solution in 1.5cubic meter of water, lasts an average of 6 hours at 90C. Thesuspension, from the reactor, is passed over a filter and the residue iswashed with 2.3 m of water.

The residue, consisting of 1024 kg, contains all the alumina, carbon,iron, titanium, magnesium, calcium and alkaline salts which were presentin the ash, together with 166 kg of silica and 3.5 kg of V The filtratecontains in solution 62 kg Na O, 14 kg SiO and 16 kg V 0 82 percent ofthe vanadium and 7.8 percent of the silica have therefore beensolubilized.

The volume of the filtrate is then reduced form 2.75 m to 1.10 m byevaporation. Then the caustic treatment is carried out with a milk oflime containg 40 kg of CaO in 0.23 m of water for 2 hours at 90C. Asolution of caustic soda is thereafter separated by decanting, afterwhich the residue is filtered and washed with 0.1 m of water. Thefiltrate combined with the washing water and the decanted solution ofcaustic soda adds up to 1.41 m of a solution of caustic soda containing62 kg Na O. To this solution, there are added 90 lofa concentratedsolution containing 54 kg of Na O to form the reacting liquor. Theprecipitate contains 16 kg V 0 14 kg SiO 40 kg CaO, 17 kg water, or indry condition, 22.8 percent of oxide: V 0

It is then put into suspension in a solution containing 35 kg of sodiumbicarbonate in 0.15 m water, and 35 kg of carbon dioxide are thereafterbubbled through this suspension, which is then filtered. Calciumcarbonate and calcium silicate separate on the filter, while vanadiumremains in the filtrate. Precipitation is carried out by bubblingthrough the solution 4 kg NH and 8 kg of CO for 10 kg of V 0 Thesolution is then filtered. The filtrate is a solution of sodiumcarbonate which is recycled after concentration by evaporation. Theresidue comprises pure ammonium vanadate which is decomposed under heat.Ammonia is recycled and 15.2 kg of vanadium oxide containing about 96% V0, are recovered.

Portion No. 2 (FIG. 3)

The reaction in the first reactors is carried out with 116 kg of Na- Oin solution in 1.5 m water for an average of 5 hours 30 minutes at 90Cand is terminated in the last reactor where a milk lime is introducedcontaining 40 kg of CaO in 0.23 m of water with suspension for 30minutes. At the exit, the suspension is passed through a filter and theresidue is washed with 2.3 m water. This residue, comprising 1,064.4 kg,contains all the alumina, iron, titanium, carbon, magnesium and alkalinesalts which were present in the mineral. The silica content is 178.4 kg,lime 66.3 kg, V 0 kg and the quantity of insolubilized caustic soda Na Ois 42 kg. The filtrate contains in solution V 0 16 kg, SiO- 1.6 kg, NaO: 74 kg. 82 percent of the vanadium and 0.9 percent of the silica havetherefore been solubilized.

The volume ofthe filtrate is reduced from 2.97 m to 8 1.12 m byvaporization, then the caustic treatment is carried out with a milk limecontaining 3 2 kg of (a0 in 0.18 m of water for 2 hours at 90C. Asolution of caustic soda is then separated by decanting, the residue isfiltered and washed over a filter with 0.1 m of water. The filtrate,combined to the washing water, is added to the solution of caustic sodawhich has been decanted. The whole comprises 1.43 m of a solution ofcaustic soda containing 74 kg of Na O, to which are added liters of aconcentrated solution containing 42 kg of Na O, to compensate for thequantity of caustic soda which has been rendered insoluble during thereaction. This solution is recycled to the first reactor.

The precipitate contains, in a dry state, 16 kg V 0 1.6 kg SiO 32 kgCaO, i.e. 32.3% V 0 It is treated like portion 1, and 15.6 kg vanadiumoxide containing 98% V 0 are finally obtained.

It is to be noted that improvements in the quantity of V 0 recovered aswell as in its purity have been made.

Moreover, only 42 kg Na O and 72 kg CaO have been consumed, instead of54 kg NaO and 40 kg Cao for the process of portion No. 1.

As the price of Na 0 is usually about five times higher than the priceof CaO, an appreciable amount of savings is achieved.

I claim 1. A process for the treatment of fly ash derived from petroleumof bituminous products to recover vanadium oxide present in the ash bythe formation of a soluble vanadate, comprising reacting the ash with asolution of caustic soda containing 1 to 5 moles of Na- O per liter forthe period within the range of 4-8 hours and a temperature within therange of between 50C and the boiling temperature ofthe solution, addingcalcium oxide to the reacting solution in an amount within the range of6-40 percent of the weight of the silica contained in the ash toprecipitate silica in the form of a calcium salt, and recoveringvanadium values.

2. The process as claimed in claim 1 in which the caustic soda solutioncontains 1 to 2 moles of Na O per liter and the reaction is carried outat a temperature within the range of C to the boiling point.

3. The process as claimed in claim 1 in which the addition of lime ismade immediately prior to the end of the reaction in order to preventprecipitation of excessive amounts of calcium vanadate.

4. The process as claimed in claim 1 in which the amount of calciumoxide added is within the range of 20-25 percent by weight of the silicacontained in the ash.

5. The process as claimed in claim 1 which includes the step of mildroasting and flotation of the fly ash to remove residual carbon.

6. The process as claimed in claim 1 in which the reaction is acontinuous reaction carried out in one or more reactors which receivethe ash and the solution of caustic soda and which includes the step offiltering the suspension formed by the reaction of the ash with thecaustic soda.

7. The process as claimed in claim 6 in which the lime is added tg thesuspension in the last of the reac tors.

8. The process as claimed in claim 1 wherein the slurry formed by thereaction of the soda with the ash is filtered, and calcium oxide isadded to the filtrate.

1. A PROCESS FOR THE TREATMENT OF FLY ASH DERIVED FROM PETROLEUM OFBITUMINOUS PRODUCTS TO RECOVER VANADIUM OXIDE PRESENT IN THE ASH BY THEFORMATION OF A SOLUBLE VANADATE, COMPRISING REACTING THE ASH WITH ASOLUTION OF CAUSTIC SODA CONTAINING 1 TO 5 MOLES OF NA2O PER LITER FORTHE PERIOD WITHIN THE RANGE OF 4-8 HOURS AND A TEMPERATURE WITHIN THERANGE OF BETWEEN 50*C AND THE BOILING TEMPERATURE OF THE SOLUTION,ADDING CALCIUM OXIDE TO THE REACTING SOLUTION IN AN AMOUNT WITHIN THERANGE OF 6-40 PERCENT OF THE WEIGHT OF THE SILICA CONTAINED IN
 2. Theprocess as claimed in claim 1 in which the caustic soda solutioncontains 1 to 2 moles of Na2O per liter and the reaction is carried outat a temperature within the range of 80*C to the boiling point.
 3. Theprocess as claimed in claim 1 in which the addition of lime is madeimmediately prior to the end of the reaction in order to preventprecipitation of excessive amounts of calcium vanadate.
 4. The processas claimed in claim 1 in which the amount of calcium oxide added iswithin the range of 20-25 percent by weight of the silica contained inthe ash.
 5. The process as claimed in claim 1 which includes the step ofmild roasting and flotation of the fly ash to remove residual carbon. 6.The process as claimed in claim 1 in which the reaction is a continuousreaction carried out in one or more reactors which receive the ash andthe solution of caustic soda and which includes the step of filteringthe suspension formed by the reaction of the ash with the caustic soda.7. The process as claimed in claim 6 in which the lime is added to thesuspension in the last of the reactors. 18
 8. The process as claimed inclaim 1 wherein the slurry formed by the reaction of the soda with theash is filtered, and calcium oxide is added to the filtrate.